As is well known in the gas turbine engine field of technology, the fuel injector utilized in a combustor of a gas turbine engine typically is mounted in the dome of the annular combustor and is judiciously located in order to assure stable and efficient combustion. The conventional fuel injector includes a fuel nozzle for injecting fuel into the combustion zone of the combustor and a swirler(s) that serves to impart vortical flow to the incoming air in order to create recirculation zones for stabilizing the combustion process. Heretofore types of fuel nozzles typically produce shear layer adjacent to two recirculation zones. The zones are divided into two separate torroidal zones, one being the inner zone and the other being the outer zone. The inner recirculation zone is located near the axis of the injector and the outer zone is located on the periphery of the swirling airflow as it dumps into the combustor. Conventional injectors insert fuel near the axis of the injector, resulting in the flame being held in the inner recirculation zone. A problem with these heretofore types of injectors and swirlers is that the flame being held in the inner recirculation zone is fuel by spray that is centrifuged outboard, thus fuel/air ratio in the inner recirculation zone. This flame-holding mode adversely affects the stabilizing characteristics of the combustion zone. The requirements to stabilize the flame are 1) a recirculation zone that positions hot combustion products near a shear layer and 2) a shear layer that mixes unburned reactants with hot combustion products.
There are a plethora of fuel nozzles that are disclosed in the prior art that include swirlers and injectors for combustors of gas turbine engines and all of which provide recirculation zones for stabilizing combustion. Examples of prior art fuel nozzles are disclosed in U.S. Pat. No. Re. 30,160 reissued in Nov. 27, 1979 and granted to Emory, Jr. et al entitled Smoke Reduction Combustion Chamber, U.S. Pat. No. 3,570,242 granted to Leonardi on Mar. 16, 1971, entitled Fuel Premixing For Smokeless Jet Engine Main Burner, U.S. Pat. No. 4,991,398 granted to Clark et al on Feb. 12, 1991 entitled Combustor Fuel Nozzle Arrangement and U.S. Pat. No. 5,603,211 granted to Graves (a co-inventor of this patent application) on Feb. 18, 1997 entitled Outer Shear Layer Swirl Mixer For a Combustor, all of which are commonly assigned to United Technologies Corporation, the assignee of this patent application. Additional patents of interests are U.S. Pat. No. 3,853,273 granted to Bahr et al on Dec. 10, 1974 entitled Axial Swirler Central Injection Carburator, U.S. Pat. No. 3,901,446 granted to Petreikis, Jr. on Aug. 26, 1975 entitled Induced Vortex Swirler, U.S. Pat. No. 4,194,358 granted to Stenger on Mar. 25, 1980 entitled Double Annular Combustor Configuration and U.S. Pat. No. 4,842,197 granted to Simon et al on Jun. 27, 1989 entitled Fuel Injection Apparatus And Associated Method.
The most relevant of these prior art patents is the U.S. Pat. No. 5,603,211 patent, supra, which discloses a three swirl passage arrangement coaxially disposed relative to the injector. Of significance is that the first and second swirl passage of this design is counter rotating and that the air mass ratio between the first and second passage is 83:17 to 91:9 and the swirl angle of the swirler in creating the counter rotating swirl is in the range of 68.degree. to 75.degree. and the mass of the airflow in the third passage which is co-rotating with the first passage is no greater than 30% of the sum of the mass of the airflows in the first second and third passages (.congruent.15%). By attaining these parameters, the results show that the combustor enhances smoke retardation and relight stability.
This invention addresses the problem of preventing lean blowout of the combustor by providing judicious design and flow characteristics to a dual swirler assembly having discrete swirl angles and mass flow ratios that permit the use of an injector of the pressure atomizing or blast type to operate at lower combustor pressure and lower injector fuel-air ratios. The assembly is limited to a dual passage swirler having an inner swirl passage with approximately a flow angle of 45.degree. to 55.degree. and in the order of 75% of the total fuel nozzle airflow, either being co-rotational or counter-rotational and the length over dome height (L/D) of the combustion air hole location is substantially equal to 0.6 characteristics. In this invention, similar to the disclosure in the U.S. Pat. No. 5,603,211 patent, the prefilm wall discharges fuel near the outer shear layer.
Actual tests of fuel nozzles comparing lean blowouts between the inner shear layer flame of the type in the prior art and the outer shear layer flame as disclosed in this invention, result in the outer shear layer flame producing blowout fuel-air ratios approximately half of the inner shear layer blowout levels. During altitude testing, the blowout pressures for a given airflow were significantly reduced for outer shear layer flames as compared to inner shear layer flames.